The invention relates to a method of recording video information in a record carrier, each picture of a sequence of pictures comprising N.times.M picture elements being divided into subpictures of n.times.m picture elements, the video information of each subpicture being encoded in accordance with a transform coding and the encoded information of the subpicture being recorded on the record carrier. The invention also relates to a method of reproducing video information from a record carrier, to apparatuses for carrying out the two methods, and to a record carrier obtained in accordance with the method of recording video information.
The article "Scene adaptive coder" by W. Chen et al in IEEE Transactions on Communications, Vol. COM-32, no. 3, March 1984 describes an apparatus for and a method of encoding video information, transmitting the encoded video information over a channel, and subsequently decoding the video information. The transform coding utilized for this purpose is the cosine transform. The following publications describe various (other) transform codings which can be employed for encoding and decoding pictures.
"Transform picture coding" by P. A. Wintz, Proc. of the IEEE, Vol. 60, no. 7, July 1972, pp. 809-820 PA0 "Digital image processing" by W. K. Pratt, Wiley and Sons, Chapter 10 "Two-dimensional unitary transforms", pp. 232-247 PA0 "Discrete cosine transform" by N. Ahmed et al, IEEE Trans. on Computers, January 1974, pp. 90-93. PA0 "Interframe cosine transform image coding" by J. A. Roese et al, IEEE Trans. on Communications, Vol. COM-25, No. 11, Nov. 1977, pp. 1329-1338, and PA0 European Patent Application EP No. 123,456. PA0 an input terminal for receiving a video signal, PA0 a first unit having an input coupled to the input terminal and having an output, for dividing consecutive pictures of N.times.M picture elements into subpictures of n.times.m picture elements, PA0 a coding unit having an input coupled to the output of the first unit and having an output, for subjecting the video information of each subpicture to a transform coding, PA0 a write unit having an input, coupled to the output of the coding unit, for recording the coded information of each subpicture on the record carrier, PA0 a comparator unit, having a first input and a second input and an output, for comparing the video information (which may have been transformed already) of corresponding sub pictures of a specific picture and of a previous picture, and for determining whether the difference between the video information(which may have been transformed already) of the two subpictures exceeds or does not exceed said first value, and for producing on its output a first control signal or a second control signal, as appropriate, PA0 a first memory having an output coupled to the first input of the comparator unit, for storing the video information (which may have been transformed already) of the corresponding subpicture of the previous picture, PA0 a second unit having an input coupled to the output of the comparator unit and having an output, for producing a first motion code or a second motion code on its output, depending on the control signal from the comparator unit, PA0 a signal combination unit having a first input coupled to the output of the encoding unit, having a second input coupled to the output of the second unit, and having an output coupled to the input of the write unit, for adding the first or the second motion code to the coded video informationof the relevant subpicture of the first-mentioned picture. PA0 a read unit for reading the coded information of each subpicture from the record carrier, PA0 a decoding unit, having an input coupled to an output of the read unit and having an output, for applying a transform decoding to the coded information of each subpicture read from the record carrier, PA0 a third unit, having an input coupled to the output of the decoding unit and having an output, for deriving consecutive pictures of N.times.M picture elements from the subpictures of n.times.m picture elements, PA0 an output terminal for supplying the video signal, which output terminal is coupled to the output of the third unit, is characterized in that the read unit is constructed to read the motion code associated with each subpicture from the record carrier.
Such codings are useful because a substantial data reduction can be achieved, enabling pictures to be transmitted over a channel of limited bandwidth.
If corresponding subpictures of a plurality of consecutive pictures do not differ too much from each other is also known to subject the first subpicture to a specific basic or first transform coding and to subject the corresponding subpicture of the next picture to a second transform coding which, on the basis of and utilizing the results of the transform coding applied to the first subpicture, provides a more accurate coding of the corresponding subpicture of the next picture, etc. After decoding this results in a subpicture of the next picture having a higher accuracy and being better in conformity with the relevant subpicture prior to coding. Such coding and decoding methods are referred to as interframe coding and decoding and are described in for example:
Thus, the use of data compression enables the playing time of a record carrier to be extended. Possibilities to do so include the (aforementioned) interframe coding or an intrafield/frame coding. The data compression attainable with intrafield/frame coding (being a two-dimensional coding) is not as high as that attainable with interframe coding. Intrafield/frame coding, however, does not give rise to any problems with trick modes (record-carrier transport at a higher or lower speed). This is because in intrafield coding each field and in interframe coding each frame or picture unit. Interframe coding problems are encountered if trick (comprising two fields) is encoded and decoded as a separate modes are to be utilized. This is because interframe coding uses the correlation between (sub-)pictures at different instants. Therefore, interframe coding is a three-dimensional coding (namely in the space and time domain).